Imaging system and pixel defect correction device

ABSTRACT

An imaging system including: an imaging device; a light blocker for blocking a light receiving section of the imaging device from light; a pixel defect correction section configured to detect and correct defective pixels of the imaging device; a signal processing section configured to process a pixel signal corrected by the pixel defect correction section; and a control for controlling the signal processing section and the light blocker according to information obtained by the pixel defect correction section. The pixel defect correction section has a timing section and measures an operating time with the timing section to estimate a secondary defect count.

RELATED APPLICATION DATA

This application is a division of U.S. patent application Ser. No.11/869,442, filed Oct. 9, 2007, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentapplication claims the benefit of priority to Japanese PatentApplication JP 2006-279963 filed with the Japan Patent Office on Oct.13, 2006 and Japanese Patent Application JP 2007-017884 filed with theJapan Patent Office on Jan. 29, 2007, the entirety both of which areincorporated by reference herein to the extent permitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to a pixel defect correction device usinga solid-state imaging device (element) and an imaging system using thesame.

Pixel defects in a CCD (Charge Coupled Device), CMOS (ComplementaryMetal Oxide Semiconductor) or other solid-state imaging device(element), or an imaging system (also described as a “camera apparatus”)using the same, can be classified into two types; crystal defectsoccurring before the shipment as in the manufacturing process andsecondary defects which occur after the shipment. Various defectcorrection methods have been proposed to prevent image deteriorationcaused by these defects.

For example, secondary defects which may develop after shipment of asolid-state imaging device (element) or imaging system are on the riseas a result of higher pixel densities achieved in solid-state imagingdevices (elements). Therefore, dynamic defect detection and correctionmethods are popular as there are no limitations to the correction count.

In a dynamic defect detection or correction of a solid-state imagingdevice (element) or imaging system, however, discrimination between highfrequency components and pixel defects involves considerabledifficulties. As a result, a high frequency component may be mistakenfor a defect. Such a determination leads to overcorrection, erroneouslyeliminating a line or point which should exist from the image if such aletter or point contains a high frequency component.

For defect correction of a solid-state imaging device (element) orimaging system, it is common, at the time of shipment, to clamp theluminance level and perform detection and correction statically withlight completely blocked or light of a given luminance admitted becausethis suppresses erroneous detection or correction.

For secondary defects of a solid-state imaging device (element) orimaging system, it is common to perform dynamic detection and correctionwithout limiting a correction count because of secondary defects on therise as a result of higher pixel densities achieved. Moreover, setupchange or readjustment after the installation is difficult depending onthe installation location of the imaging system.

SUMMARY OF THE INVENTION

Adjustments such as defect detection and correction at power-on havebeen a prerequisite for product shipment. In monitoring imaging andother systems, however, setup change or readjustment after theinstallation is difficult depending on the installation location. As aresult, second defects at the time of shipment or after the installationmay not be dealt with. Further, higher pixel densities achieved insolid-state imaging devices (elements) have led to an increased pixelcount. This in turn has resulted in a growing number of secondarydefects. Thus, it is becoming common to correct secondary defectsthrough dynamic defect detection and correction which unlimited in termsof a correction count. In dynamic defect detection and correction,however, discrimination between high frequency components and pixeldefects involves difficulties. As a result, a high frequency componentmay be mistaken for a defect. This leads to overcorrection, erroneouslyeliminating a line or point which should exist if it contains a highfrequency component and making it impossible to visually identify theline or point. Further, if that line or point is a feature point of thesubject, the image will become corrupted.

Defect detection and correction as necessary during image capture orreproduction, on the other hand, results in a corrupted display image asthis corrects defective pixels of the on-screen image.

A solid-state imaging device may develop secondary defects after itsshipment or the shipment of an imaging system (camera apparatus)incorporating the imaging device. In light of the above, it is desire ofthe present invention to properly restrict overcorrection. To achievethis desire, according to the present embodiment, the operating time ofa solid-state imaging device or an imaging system (camera apparatus)using the same is measured with a timer counter (timing section). Morespecifically, the operating time from the moment of static detection orcorrection of secondary defects is measured. Next, a secondary defectcount distribution is calculated based on the defect rate of thesolid-state imaging device and the imaging system and its operatingtime. Then, an overcorrection determination threshold value is set forthe calculated secondary defect count distribution. Finally, a settingsuch as market defect rate is assigned to determine an appropriatecorrection count, thus properly restricting overcorrection. It isanother desire of the present invention to perform static defectcorrection when defect correction will not affect the on-screen image aswhen there is no need to record images at given time intervals or duringimage loading.

An imaging system of the present invention includes an imaging device,light blocking means for blocking a light receiving section of theimaging device from light, and a pixel defect correction sectionconfigured to detect and correct secondary defects of the imagingdevice. The imaging system further includes a signal processing sectionconfigured to process a pixel signal corrected by the pixel defectcorrection section and control means for controlling the signalprocessing section and the light blocking means according to pixeldefect information obtained by the pixel defect correction section. Thepixel defect correction section includes timing means and measures anoperating time with the timing means to estimate a secondary defectcount.

An imaging system of the present invention includes an imaging device,light blocking means for blocking a light receiving section of theimaging device from light, and a pixel defect detection/correctionsection configured to detect and correct defective pixels associatedwith an image obtained by the light receiving section. The imagingsystem further includes a signal processing section configured toprocess a pixel signal corrected by the pixel defectdetection/correction section and output a video signal. The imagingsystem still further includes control means for obtaining video motioninformation by finding the stability of the video signal from the signalprocessing section, blocking the imaging device from light bycontrolling the light blocking means according to the change in video,and detecting and correcting defective pixels with the imaging deviceblocked from light.

A pixel defect detection/correction device of the present inventionincludes pixel defect detection means for being supplied with a pixelsignal, detecting defects of the pixel signal, and measuring a defectcount. The pixel defect detection/correction device further includestiming means. The pixel defect detection/correction device still furtherincludes an overcorrection calculation section. The overcorrectioncalculation section compares a measured value of the pixel defectdetection means with an estimated value of the pixel signal after theelapse of a predetermined time measured by the timing means. By doingso, the same section determines whether the defect correction is anovercorrection. If so, the same section generates a control signal tocorrect the defective pixels. The pixel defect detection/correctiondevice corrects defects of the pixel signal with the control signal fromthe overcorrection calculation section.

A pixel defect detection/correction device of the present inventionincludes pixel defect detection means for being supplied with a pixelsignal, detecting defects of the pixel signal, and measuring a defectcount. The pixel defect detection/correction device further includes anovercorrection calculation section. The overcorrection calculationsection compares a detected value of the pixel defect detection meanswith an estimated defect count of the pixel signal after the elapse of apredetermined time measured by timing means. By doing so, the samesection determines whether the defect correction is an overcorrection.If so, the same section generates a control signal to correct thedefective pixels. The pixel defect detection/correction device stillfurther includes motion information detection means for detecting thestability of a video signal formed by the pixel signal and generating acontrol signal to perform defect detection and correction according tothe change in video. The pixel defect detection/correction device stillfurther includes a controller configured to control the operation of thepixel defect detection means and the overcorrection calculation sectionbased on the control signal from the motion information detection meansso as to detect and correct the defective pixels during a predeterminedperiod according to the change in video.

According to the present embodiment, an operating time is measured bytiming means from the moment of detection or correction of defects in animaging system. Next, a secondary defect count distribution of animaging device is calculated based on its defect rate and operatingtime. Then, an overcorrection determination threshold value is set forthe calculated secondary defect count distribution. Finally, a settingsuch as market defect rate is assigned to determine an appropriatecorrection count, thus properly restricting overcorrection. Further,this overcorrection is carried out without corrupting the on-screenimage.

A pixel defect correction device and imaging system of the presentinvention calculates an appropriate defective pixel count in an elapsedtime, thus suppressing overcorrection. The pixel defect rate variesdepending on the installation location of the imaging system. However,use of a defect rate and threshold value for overcorrectiondetermination makes it possible to suppress overcorrection properlyaccording to the location of use.

The pixel defect correction device and imaging system of the presentinvention do not require complicated circuitry or control fordetermination of overcorrection. Even if the imaging device is installedwhere readjustment is difficult, it can be readjusted at a proper timethanks to information issued following overcorrection. Once installed,the imaging system does not require readjustment of its defect detectionand correction. The imaging equipment is capable of self-recovery byitself.

Further, correction operation can be performed without corrupting theon-screen image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block configuration diagram of an imaging system;

FIG. 2 is a block configuration diagram of a digital signal processingsection illustrated in FIG. 1;

FIG. 3 is a block configuration diagram of a defect detection/correctioncircuit illustrated in FIG. 2;

FIG. 4 is a distribution diagram illustrating a calculated defectdistribution;

FIG. 5 is a flowchart for describing the operation of the imagingsystem;

FIG. 6 is a block configuration diagram of the imaging system;

FIG. 7 is a flowchart for describing the operation of the imaging systemillustrated in FIG. 6; and

FIG. 8 is a flowchart for describing the operation of the imaging systemillustrated in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a schematic configuration diagram of an imagingsystem (camera apparatus) 100 according to an embodiment of the presentinvention. The imaging system 100 includes a lens 1, an image sensor ADC(analog/digital converter) 2, a clamp circuit 3, a digital signalprocessing section 10, a controller 30 and other components.

The lens 1 has an iris (light blocking section) mechanism which is notshown in FIG. 1. The iris mechanism is controlled by an iris controlsignal from the controller 30.

The image sensor ADC 2 includes not only a solid-state imaging devicebut also an S/H (sample hold) circuit, an AGC (auto gain control)circuit, an ADC converter and other components.

The digital signal processing section 10 includes a defectdetection/correction circuit 4 and a signal processing section 5.Further, the defect detection/correction circuit 4 includes a defectcorrection section 4A and a defect detection section 4B as illustratedin FIG. 2. The signal processing section 5 includes a signal processingcircuit 11, an encoder 12 and other components.

The controller 30 includes control circuits, a microcomputer and othercomponents. For example, the microcomputer controls the operation of thelens 1's iris, and the defect detection/correction circuit 4 and thesignal processing section 5 of the digital signal processing section 10.

In addition to the above, a timing generator which is not shown in FIGS.1 and 2 generates control signals including horizontal and verticalclock signals with reference to a system clock, thus driving the imagesensor ADC 2 and the digital signal processing section 10 atpredetermined timings.

In the imaging system 100 configured as described above, the lens 1forms the image of a subject not shown in FIG. 1 on the imaging surfaceof the image sensor ADC 2. A solid-state imaging device such as CCD orCMOS imaging device is generally used for the image sensor ADC 2. Theimage sensor (ADC) 2 converts the image formed on its imaging surfaceinto an electric signal on a pixel-by-pixel basis and supplies thissignal as an imaging signal to an S/H & AGC circuit which is not shownin FIGS. 1 and 2.

The S/H & AGC circuit samples and holds an imaging signal from thesolid-state imaging device of the image sensor ADC 2 to extractnecessary data. At the same time, the S/H & AGC circuit regulates thegain of the imaging signal to adjust it to a proper level. The outputsignal of the S/H & AGC circuit is supplied to the A/D converter.

The A/D converter converts the output signal of the S/H & AGC circuitfrom analog to digital to the clamp circuit 3. The A/D convertersupplies, for example, 10-bit data to the clamp circuit 3.

The clamp circuit 3 clamps the black level of the imaging signal indigital form at a predetermined voltage level first and then suppliesthe signal to the digital signal processing section 10.

The digital signal processing section 10 supplies the digital data fromthe A/D converter to the defect detection/correction circuit 4.

The defect detection/correction circuit 4 making up the main part of apixel defect correction device includes the defect correction section 4Aand the defect detection section 4B as illustrated in FIG. 2. The defectcorrection section 4A corrects defective pixels using a correction pulsefrom a correction pulse generation circuit 27. On the other hand, anovercorrection calculation section 50 of the defect detection section 4Bsuppresses overcorrection on defective pixels. Based on defective pixeladdress data resulting from overcorrection suppression, the correctionpulse generation circuit 27 generates a correction pulse which issupplied to the defect correction section 4A. Overcorrected defectivepixels are corrected by the defect correction section 4A. Theovercorrection calculation section 50 may include software and beimplemented by causing the controller to write address data back to aRAM 23 which stores defective pixel addresses.

Defective pixels are corrected by correcting pixel values by one of thepublicly known interpolation methods. In one of the methods, the pixelof interest is replaced by the immediately preceding pixel or the pixelbefore the immediately preceding pixel in real time. In another method,the pixel of interest is replaced by the mean value of the immediatelypreceding and succeeding pixels. In still another method in which pixelsin the vertical direction are considered, the pixel of interest isreplaced by the pixel immediately above it or by the mean value of thepixels immediately above and below it.

The signal processing section 5 includes a YC separation circuit, aluminance signal processing section, a color signal processing sectionand other components which are not shown in FIGS. 1 and 2. The samesection 5 separates the image signal subjected to defect correction intoa luminance signal (data) and color signal (data) with the YC separationcircuit. Then, the luminance signal undergoes predetermined signalprocessing by the luminance signal processing section. The color signalundergoes predetermined signal processing by the color signal processingsection.

The luminance signal processing section handles various types of imageprocessing including vertical and horizontal contour correction and γ(gamma) correction of the Y (luminance) signal.

The color signal processing section handles processing including removalof noise and false color from the color signal, RGB matrix processing,white balance adjustment in which RGB factors are changed, γ (gamma)correction, R-G/B-G conversion, color difference signal (Cr/Cb)generation and hue/gain adjustment.

The signal processing section 5 is supplied with color differencesignals R-Y and B-Y from the color signal processing section. The samesection 5 is also supplied with a luminance signal Y from the luminancesignal processing section. The same section 5 adds a synchronizingsignal to the above signals to output an analog composite signal. Inaddition to the analog composite signal, the same section 5 also outputsan analog component signal, a digital component signal and othersignals.

The imaging system 100 illustrated in FIG. 1 will be described next. Thelens 1 forms the image of a subject not shown in FIG. 1 on the imagingsurface of the imaging device of the image sensor ADC 2. The imageformed on the imaging surface of the solid-state imaging device isconverted into an electric signal on a pixel-by-pixel basis andsupplied, as an imaging signal, to the S/H & AGC circuit which is notshown in FIG. 1.

The S/H & AGC circuit samples and holds the imaging signal from thesolid-state imaging device to extract necessary data. At the same time,the S/H & AGC circuit regulates the gain of the imaging signal to adjustit to a proper level. After the gain control, the output signal of theS/H & AGC circuit is supplied to the A/D converter.

The A/D converter converts the analog signal into digital form. Theblack level of the imaging signal in digital form is clamped by theclamp circuit 3 at a predetermined voltage level. Then, the resultantsignal is supplied to the digital signal processing section 10.

The digital data from the clamp circuit 3 is supplied to the defectdetection/correction circuit 4 (4A and 4B) of the digital signalprocessing section 10.

The defect detection/correction circuit 4 or the controller 30 has atimer for timing purposes. The timer is set when a static defectcorrection is performed at the time of or after the shipment. The timeris set, for example, to count the time when pixel defect correction isto be performed next time. When the set time comes, pixel defectcorrection will be automatically performed. Alternatively and inaddition to the above, information is issued externally by an audio orvisual prompt via the controller 30 that the user can adjust the imagingsystem 100.

In the pixel defect correction, a defective pixel count is calculatedfirst from a defect rate calculated in advance for the elapsed time setwith the timer. Further, a permissible pixel count is added to thecalculated defective pixel count to set a threshold value.

Next, the threshold value is compared with the defective pixel countdetected by the defect detection section 4B to determine whether thecorrection for the elapsed time is appropriate or it is anovercorrection.

After overcorrection control by the overcorrection calculation section50 of the defect detection section 4B which will be described later, acorrection pulse is generated based on defective pixel address data.This correction pulse is supplied to the defect correction section 4Afor correction of defective pixels.

Based on defect information from the controller 30, a correction pulseis supplied to the defect correction section 4A of the defectdetection/correction circuit 4, thus allowing defective pixels to becorrected.

Defective pixels are corrected by correcting pixel values by one of thepublicly known interpolation methods. In one of the methods, the pixelof interest is replaced by the immediately preceding pixel or the pixelbefore the immediately preceding pixel in real time. In another method,the pixel of interest is replaced by the mean value of the immediatelypreceding and succeeding pixels. In still another method in which pixelsin the vertical direction are considered, the pixel of interest isreplaced by the pixel immediately above it or by the mean value of thepixels immediately above and below it.

A properly corrected image signal undergoes YC separation by the signalprocessing section 5 first followed by predetermined signal processingby the luminance signal processing section, the color signal processingsection and other components. Then, the encoder 12 encodes the colordifference signals R-Y and B-Y and the luminance signal Y and adds asynchronizing signal to the resultant signal to output an analogcomposite signal.

Next, FIG. 2 illustrates a block configuration of the digital signalprocessing section 10 in an embodiment of the present invention. Thedigital signal processing section 10 includes the defectdetection/correction circuit 4, the signal processing section 5 andother components. The defect detection/correction circuit 4 includes thedefect correction section 4A and the defect detection section 4B. Thesignal processing section 5 includes the signal processing circuit 11and the encoder 12.

In the defect correction section 4A, defective pixels are corrected bycorrecting pixel values by one of the publicly known interpolationmethods. In one of the methods, the pixel of interest is replaced by theimmediately preceding pixel or the pixel before the immediatelypreceding pixel in real time. In another method, the pixel of interestis replaced by the mean value of the immediately preceding andsucceeding pixels. In still another method in which pixels in thevertical direction are considered, the pixel of interest is replaced bythe pixel immediately above it or by the mean value of the pixelsimmediately above and below it.

Next, the defect detection section 4B will be described. As illustratedin FIG. 2, the defect detection section 4B includes, for example, acomparator 21, an address detection circuit 22, a RAM (Random AccessMemory) 23, a counter 24, a level setting circuit 25, the overcorrectioncalculation section 50, the correction pulse generation circuit 27 andother components. Part of the overcorrection calculation section 50 maybe provided in the controller 30 and configured, for example, withsoftware.

The comparator 21 compares the output level of the CCD (or CMOS) imagesensor ADC 2 in frame readout mode, with a predetermined level (valueset with the level setting circuit 25) to detect defective pixels.

The address detection circuit 22 identifies defective pixel addressesbased on the detection output of the comparator 21 and converts thisframe-read address into a field-read address.

The RAM 23 is provided to hold detection results of defective pixels inthe form of address data. The RAM 23 stores address data from theaddress detection circuit 22 on a field-by-field basis for odd- andeven-numbered fields.

The counter 24 successively measures the number of defective pixelswhose amplitude is detected to be equal to or exceed a predeterminedlevel by the comparator 21.

The level setting circuit 25 sets a pixel level used to determinedefective pixels.

The overcorrection calculation section 50 determines a defective pixelcorrection count, for example, by calculating a defect rate, measuringthe operating time and setting an overcorrection determination thresholdvalue. The overcorrection calculation section 50 will be describedlater.

The correction pulse generation circuit 27 generates a control signal tocorrect overcorrected pixels in response to a control signal from theovercorrection calculation section 50 and supplies the control signal tothe defect correction section 4A.

Following YC separation, the signal processing circuit 11 handlescontour correction, γ (gamma) correction and other processing of theluminance signal. The same circuit 11 handles, for example, whitebalance adjustment and matrix processing of the color signal to generatecolor difference signals.

The encoder 12 is supplied with a luminance signal processed by theluminance signal processing section and a color signal processed by thecolor signal processing section. The encoder 12 adds a synchronizingsignal to these signals and outputs, for example, a composite signal.

The imaging system (camera apparatus) 100 illustrated in FIG. 1 will bedescribed next with reference to FIG. 2. When the imaging system 100configured as described above is started, the timer built into thecontroller 30 or provided in the overcorrection calculation section 50of the digital signal processing section 10 is set. Once set, the timerstarts counting the operating time of the imaging system 100.

When the set time elapses, the defect detection/correction circuit 4activates the overcorrection suppression function under the control ofthe controller 30. An image signal is supplied to the defectdetection/correction circuit 4 from the clamp circuit 3. The comparator21 of the defect detection/correction circuit 4 compares the imagesignal level with a predetermined reference signal level. When the imagesignal level is smaller than the reference signal level, no outputsignal such as pulse is output to the counter 24. That is, the counter24 does not count the number of defective pixels. Further, the addressdetection circuit 22 does not detect address data of defective pixels.As a result, no address data is output to the RAM 23.

On the other hand, if the image signal level is found to be greater thanthe reference signal level by the comparator 21, an output signal suchas pulse is supplied to the counter 24, causing the counter 24 to countthe number of defective pixels. At the same time, the address detectioncircuit 22 detects address data of defective pixels. This address datais output to the RAM 23 for storage.

The overcorrection calculation section 50 calculates the defect countbased on the pixel defect rate at the user-set time or the time set inadvance. This defect rate is determined, for example, from paststatistical data relating to defective pixels. This defect rate isstored, for example, in a storage device of the controller 30.

The defective pixel count obtained by the counter 24 is compared withthe estimated defective pixel count (threshold value) calculated by theovercorrection calculation section 50. This determines whether thedefect correction is an overcorrection, namely, whether more pixels werecorrected than the calculated number of defective pixels to becorrected.

When the defect correction is not an overcorrection, no furthercorrection will be made. On the other hand, if it is found that morepixels were corrected than the calculated number of defective pixels tobe corrected, information about defect correction and readjustment(defect information) is issued via the controller 30, thus calling theuser's attention. In response to this information, the user will proceedwith adjustment or repair of the imaging system.

Further, in the case of overcorrection, the iris in the lens 1 isautomatically adjusted via the controller 30. In this adjustment, thesolid-state imaging device (element) of the image sensor ADC 2 isblocked from light to measure the black level and detect white defects.Then, overcorrection is readjusted to achieve self-recovery.

As another readjustment method, the defect detection and correction maybe readjusted automatically using the motion detection function duringan interval (period) free from moving objects.

As still another readjustment method, the defect detection andcorrection may be readjusted during a mute period of video output signalsuch as mode transition period.

The overcorrection calculation section 50 of the pixel defect correctiondevice illustrated in FIG. 3 will be described next. The overcorrectioncalculation section 50 includes a timer counter (timing section) 51, adefect distribution calculation section 52, a threshold value settingcircuit 53 and a correction calculation section 54. It should be notedthat each of these functional blocks can be implemented not only withhardware but also with the controller 30 illustrated in FIG. 1. Inparticular, the microcomputer's clock may serve as the timer counter 51.The operating time of the imaging system 100 can be stored, for example,in the RAM incorporated in the controller 30. Here, a description willbe made of a case where the overcorrection calculation section 50 isconfigured with hardware.

The timer counter 51 measures the operating time of the imaging system100 by a control signal form the controller 30.

When the operating time measured by the timer counter 51 reaches a settime, operating time information is supplied to the defect distributioncalculation section 52.

The defect distribution calculation section 52 calculates a defectivepixel count for the operating time based on the defect rate and thepixel count of the image sensor ADC 2. The defect rate is known toincrease in a linear function of operating time. The timer is reset tomeasure the operating time again when the imaging system 100 isreadjusted, for example, by the user at the time of or after theshipment.

A statistical distribution curve of the defect rate is generally aGaussian distribution curve as illustrated in FIG. 4. The curve plotsthe distribution ratio in arbitrary unit on the vertical axis versus thedefect count on the horizontal axis.

The threshold value setting circuit 53 sets a pixel count as anovercorrection threshold value. This pixel count is obtained by adding apermissible count to the defective pixel count for the operating timesupplied from the defect distribution calculation section 52. Thispermissible level is set according to the operating conditions of theimaging system 100 including the location and temperature. Setting athreshold value for determination of overcorrection makes it possible toproperly restrict overcorrection of defects.

The correction calculation section 54 is supplied with an overcorrectionthreshold value from the threshold value setting circuit 53 and adefective pixel count and addresses of the defective pixels from thecounter 24 and the RAM 23. The defective pixel count is compared withthe overcorrection threshold value to determine whether overcorrectionhas occurred. If so, a control signal is output to the overcorrectioncalculation section 50 to prevent overcorrection. At the same time, acontrol signal is output via the controller 30 to suppressovercorrection.

On the other hand, if it is determined that overcorrection has notoccurred, normal image defect correction is maintained.

The operation of the overcorrection calculation section 50 will bedescribed next. When a predetermined operating time, set with the timercounter 51 at the time of shipment or previous adjustment of the imagingsystem 100, elapses, the defective pixel count generally increasesproportionally to the operating time. Therefore, the defective pixelcount can be estimated from a statistical distribution. A defectivepixel count measured by the counter 24 is compared with anovercorrection threshold value. This threshold value takes into accountthe defective pixel count estimated by statistical processing and apermissible defective pixel count. When the defective pixel countmeasured by the counter 24 is smaller than the overcorrection thresholdvalue, this means that adjustment has been made properly. Therefore, theovercorrection calculation section 50 outputs no control signal to thecorrection pulse generation circuit 27 to suppress overcorrection. Atthis time, normal correction is carried out by the defect correctionsection 4A. Therefore, no adjustment for overcorrection will be made.

On the other hand, the defective pixel count is measured by counter 24after the elapse of the operating time set in the timing section (timercounter 51) by the user or administrator. If the defective pixel countis detected to be greater than the overcorrection threshold value by thecomparator 21, dynamic overcorrection may have been carried out. Thatis, if it is found that erroneous detection has occurred, the imagingsystem 100 is panned or tilted. That is, the system is movedhorizontally or vertically to move its imaging region. If the signallevel of pixels to be corrected changes with change in the subject whenthe imaging region is moved, it is determined that the pixels have beenerroneously detected. If there is no change in signal level, it isdetermined that the pixels are defective. Thus, erroneously detectedpixels can be identified. This makes it possible to remove such pixelsfrom those pixels to be checked for defect, thus suppressingovercorrection.

A possible method of suppressing overcorrection is static correctioncontrol. For example, if the secondary defect count is estimated to begreater than the overcorrection threshold value, the overcorrectioncalculation section 50 supplies a control signal to the controller 30.In response, the controller 30 controls the iris mechanism of the lens 1to block the solid-state imaging device (element) of the image sensorADC 2 from light. Then, the black level of each of the pixels of thesolid-state imaging device (element) is measured. If the measured blacklevel is greater than a predetermined level by a given level or more,the pixel of interest is determined to have a white defect. The detecteddefective pixels are readjusted for automatic self-recovery.

As an alternative method of static overcorrection control, defectdetection and correction can be readjusted, for example, during a muteperiod of video output signal. That is, readjustment can be achieved bysupplying an iris control signal to the iris control mechanism of thelens 1 from the controller 30 so as to automatically block thesolid-state imaging device (element) of the image sensor ADC 2 fromlight.

As another overcorrection control method, defect detection andcorrection may be readjusted using the motion detection function of theimaging system 100 during a period free from moving objects. Thisprevents moving objects from being overlooked, thus ensuring properdefect correction at all times.

In addition to automatic overcorrection control, on the other hand,issuing information to external equipment to prompt the readjustmentmakes it possible for the administrator to readjust the imaging system100. For example, if, as a result of comparison of a defect countmeasured by the overcorrection calculation section 50 in a predeterminedoperating time with an overcorrection threshold value estimated bystatistical processing for the operating time, the defect count isgreater than the threshold value, the overcorrection calculation section50 outputs a control signal to the controller 30 via an interface.

The controller 30 transfers the control signal to a display device ofthe imaging system 100 which is not shown. As a result, a messageindicating that defect correction may be required appears on thisdisplay section. If the administrator can readjust the defect detectionand correction from external equipment after seeing the message, he orshe will do so at a proper time to maintain the imaging system 100corrected properly at all times.

Next, FIG. 5 illustrates a flowchart for readjusting the overcorrectionof the imaging system 100.

In step ST-10, pixel defect correction is performed at the time of orafter the shipment. This pixel defect correction may be static ordynamic.

In step ST-12, the time information resulting from the defect correctionin step ST-10 is stored in the timer counter of the controller 30 orthat of the overcorrection calculation section 50. At the same time, thetimer counter is set so that defect correction can be performed in agiven operating time.

In step ST-14, when the given operating time of the imaging system 100elapses, the controller 30 issues an instruction. In response to thisinstruction, a pixel defect rate of the solid-state imaging device ofthe image sensor ADC 2 is estimated for this operating time fromstatistical distribution. Based on the estimated ratio, the defectivepixel count is calculated in the total pixel count of the solid-stateimaging device of the image sensor ADC 2.

In step ST-16, an overcorrection threshold value (defective pixel count)is found from the estimated defect count. The threshold value takes intoaccount a permissible count.

In step ST-18, the defective pixel count is compared with the estimatedovercorrection threshold value.

If the defect correction is determined to be an overcorrection becausethe defective pixel count is greater than the estimated threshold valuein step ST-18, overcorrection will be suppressed. Alternatively, thecontroller 30 will issue a request for defective pixel correction sothat the administrator can readjust the imaging system (step ST-22).

When the defect correction is determined not to be an overcorrectionbecause the defective pixel count is smaller than the estimatedthreshold value in step ST-18, control returns to step ST-14 (stepST-20). Thereafter, the same process steps will be repeated.

As described above, the defect detection/correction circuit and imagingsystem calculate an appropriate defective pixel count over time, thussuppressing overcorrection. The pixel defect rate varies depending onthe installation location of the imaging system. However, use of adefect rate and a threshold value for overcorrection determination makesit possible to suppress overcorrection properly according to thelocation of use. Further, a request is issued to external equipment toreadjust overcorrection, thus permitting readjustment.

Next, the defect correction not affecting the on-screen image will bedescribed with reference to FIG. 6. An imaging system illustrated inFIG. 6 includes some additional functional blocks as compared to theimaging system 100 illustrated in FIG. 1.

The digital signal processing section 10 further includes a stabilitydetection circuit 13. In addition, a memory 20 and an external sensor 40have been added as part of the system.

Hereinafter, the description of the same blocks as those in FIG. 1 willbe omitted, and the blocks different therefrom will be described.

The stability detection circuit 13 is connected to the signal processingsection 5 of the digital signal processing section 10 and to thecontroller 30. The stability detection circuit 13 includes a luminanceintegration circuit, color integration circuit, motion detection circuitand other circuitry. The luminance integration circuit integrates aluminance signal from the signal processing section 5. The colorintegration circuit integrates a color signal from the same section 5.The motion detection circuit detects a subject motion by detecting thesubject position from one field or frame to the next based on the imagefrom the same section 5.

The memory 20 is connected between the input and output of the signalprocessing section 5 of the digital signal processing section 10. Thememory 20 stores image data from the same section 5. The memory 20supplies stored image data to the same section 5 at a predeterminedtiming in response to a control signal from the controller 30. Forexample, the memory 20 outputs image data or a given image to thedisplay device during a correction period.

The controller 30 detects and controls a subject obtained by theexternal sensor 40. In addition, the controller 30 is supplied withdetection information from the motion detection circuit and motioninformation from the luminance and color integration circuits. If thedetection information indicates that there are no moving objects or ifthe motion information indicates that there is no motion of luminance orcolor component, the controller 30 controls the lens 1, the defectdetection/correction circuit 4 and the signal processing section 5.Further, the controller 30 exchanges data with the defectdetection/correction circuit 4, the signal processing section 5 and thestability detection circuit 13 of the digital signal processing section10 and the external sensor 40 to control these circuits and componentbased on the data.

The external sensor 40 includes, for example, an ultrasonic, infrared orCCD sensor. The same sensor 40 senses the presence or absence of asubject in front of the imaging system and supplies the sensing resultto the controller 30.

Next, the operation of the imaging system 100A illustrated in FIG. 6will be described. The lens 1 forms the subject image on the imagingsurface of the image sensor ADC 2. The image is converted into anelectric signal on a pixel-by-pixel basis and output as an imagingsignal. After sampling and holding, the analog signal is converted intoa digital signal by the A/D converter. The digital imaging signal isclamped by the clamp circuit 3 at a predetermined voltage level. Then,the resultant signal is supplied to the digital signal processingsection 10. On the other hand, digital data from the clamp circuit 3 issupplied to the defect detection/correction circuit 4 of the digitalsignal processing section 10.

The defect detection/correction circuit 4 or the controller 30 has atimer for timing purposes. The timer is set when a static defectcorrection is performed at the time of or after the shipment. The timeris set, for example, to count the time when pixel defect correction isto be performed next time. When the set time comes, pixel defectcorrection will be automatically performed. Alternatively and inaddition to the above, information is issued externally by an audio orvisual prompt via the controller 30 so that the user can adjust theimaging system 100A.

Next, the defect detection and correction operation will be described.This operation is readjusted at different timings (and periods).Readjustment thereof is accomplished by detecting a period when theon-screen image will not be affected, blocking the CCD device from lightwith a mechanical iris or other light blocking mechanism during thatperiod and detecting and correcting defective pixels statically duringthat light blocking period.

More specifically, there are three defect detection and correctiontimings (and periods). The first timing and period are when there is nochange in video signal with no need to record the video signalcontinuously. The second timing and period are when video may not becontinuously obtained as during a mode transition or mute period. Thethird timing and period are when video is kept static as during loadingof still image.

Firstly, a case will be described where defective pixels are detectedand corrected during a period when there is no change in video signalwith no need to record the video signal continuously.

Luminance and color signals from the signal processing section 5 aresupplied to the stability detection circuit 13 (luminance integration,color integration and motion detection circuits). The luminance signalis integrated by the luminance integration circuit. The color signal isintegrated by the color integration circuit which is an OPD (opticaldetector). A period is detected when there is no change in theintegrated values of the luminance and color signals. Motion informationduring this period is supplied to the controller 30. The controller 30considers, as a correction period, a period free from motion ofluminance or color signal and outputs a control signal to the defectdetection/correction circuit 4 and the signal processing section 5.

On the other hand, if, as a result of detection by the motion detectioncircuit, there are no moving objects, the controller 30 outputs acontrol signal for defect correction to the defect detection/correctioncircuit 4 and the signal processing section 5.

Alternatively, the controller 30 detects the subject obtained by theexternal sensor 40. When determining that there are no targets to beimaged, the controller 30 outputs a control signal to the defectdetection/correction circuit 4 and the signal processing section 5 toinitiate correction control.

Secondly, a case will be described where defective pixels are detectedand corrected during a period when video may not be continuouslyobtained as during a mode transition or mute period.

Upon detection of the activation of the pixel count change modeavailable with the imaging system 100A, the controller 30 outputs acontrol signal to the defect detection/correction circuit 4 and thesignal processing section 5, thus initiating correction control.

Further, the mute operation starts when the format is switched betweenJPEG (Joint Photographic Experts Group) and MPEG (Motion Picture ExpertsGroup) or when the broadcasting system is switched between NTSC(National Television System Committee), PAL (Phase Alternation by LineColor Television) and SECAM (Sequential Couleur a Memoire). In additionto the above, the mute function is activated when video display is notdesired so that the display screen is switched to monochrome (e.g.,black, blue).

When the mute operation is activated, the controller 30 detects theactivation or start timing of the operation and outputs a control signalto the defect detection/correction circuit 4 and the signal processingsection 5. This causes the same circuit 4 to initiate the defectcorrection operation.

Thirdly, a case will be described where defective pixels are detectedand corrected during a period when video is kept static as duringloading of still image.

During loading of a still image, an integrated value of luminance orcolor signal does not indicate any motion of the subject. Therefore, thestatus of the loaded image is detected. Then, the motion informationobtained therefrom is supplied to the controller 30. The controller 30considers, as a pixel defect correction period, a period during whichvideo is kept static as during loading of still image, and outputs acontrol signal to the defect detection/correction circuit 4 and thesignal processing section 5. Alternatively, if it is found, as a resultof detection of the (still) image by the motion detection circuit, thatthere are no moving objects, the controller 30 outputs a control signalto the defect detection/correction circuit 4 and the signal processingsection 5. This initiates the defect detection and correction operationof the same circuits 4 and 5.

When any of the above three detect detection and correction timings (andperiods) comes, the controller 30 supplies an iris control signal to theiris mechanism of the lens 1, thus blocking the solid-state imagingdevice of the image sensor ADC 2 from light. When the solid-stateimaging device is blocked from light, the image sensor ADC 2 suppliespixel data of its imaging device to the defect detection/correctioncircuit 4 via the clamp circuit 3. The defect detection/correctioncircuit 4 detects the output level of all pixels. Based on thisdetection result, defective pixels and their addresses are identified.

In the pixel defect detection and correction operation, a defectivepixel count (defect count) is calculated first based on the defect ratecalculated in advance for the elapsed time set by the timer. Further, athreshold value is set which is obtained by adding a permissible pixelcount to the calculated defective pixel count (calculated correctioncount).

Next, the threshold value is compared with the defective pixel countdetected by the defect detection section 4B to determine whether thecorrection is appropriate for the elapsed time or an overcorrection.

Overcorrection control is performed on the defective pixels by theovercorrection calculation section 50 of the defect detection section 4Bwhich will be described later. Then, a correction pulse is generatedbased on the address data of the defective pixels. This correction pulseis supplied to the defect correction section 4A for correction of thedefective pixels.

Based on defect information from the controller 30, a correction pulseis supplied to the defect correction section 4A of the defectdetection/correction circuit 4 for correction of the defective pixels.

Defective pixels are corrected by correcting pixel values by one of thepublicly known interpolation methods. In one of the methods, the pixelof interest is replaced by the immediately preceding pixel or the pixelbefore the immediately preceding pixel in real time. In another method,the pixel of interest is replaced by the mean value of the immediatelypreceding and succeeding pixels. In still another method in which pixelsin the vertical direction are considered, the pixel of interest isreplaced by the pixel immediately above it or by the mean value of thepixels immediately above and below it.

The video display operation during a defect correction period will bedescribed next.

When the controller 30 supplies a control signal for defect detectionand correction to the signal processing section 5, a timing and periodare set at which to interpolate a video signal from the signalprocessing section 5. At the same time, the video signal from the signalprocessing section 5 is stored in the memory 20. The image data storedin the memory 20 during a defect correction period is read and output tothe display device via the signal processing section 5. That is, onlythe image before correction output from the memory 20 is displayedduring this defect detection and correction period. Thus, the imagebeing corrected is not displayed.

This ensures that no corrupted video signal from the signal processingsection 5 is displayed, thereby allowing for correction without causingany discomfort to the user.

Next, FIG. 7 illustrates a flowchart for describing the static defectdetection and correction operation during normal operation of theimaging system 100A.

In step ST-30, a pixel defect correction is performed at the time of orafter the shipment, followed by normal operation. We assume that thispixel defect correction is a static correction.

After the defect correction, time information is stored in the timercounter of the controller 30 or that of the overcorrection calculationsection 50. This allows a defect correction to be performedautomatically in a predetermined operating time.

In step ST-32, it is determined whether the overcorrection calculationsection 50 has made a request for defect detection and correctionoperation. If no request has been made, no correction will be performed.In this case, the camera will continue, for example, its monitoringoperation.

Alternatively, a request may be made by external equipment rather thanthe overcorrection calculation section 50. More specifically, a requestcan be made for defect detection and correction operation according to acontrol program by transferring commands to the control section such asCPU (microcomputer) by key operation. Further, a defect correctionrequest signal can be generated by pressing the control button so as tooperate the hardware.

In step ST-34, when a request is made for defect detection andcorrection operation after the time set by the timer counter elapses, itis determined whether video recording may be required. If so, no defectcorrection will be performed. That is, a defect detection and correctiontiming is detected.

In step ST-36, when video recording is not required, video output isheld in the memory 20. At the same time, the controller 30 supplies acontrol signal to the iris mechanism of the lens 1.

During this period, a video (image) signal is output from the memory 20via the digital signal processing section 10. No video (image) beingcorrected is displayed.

In step ST-38, the iris is controlled so that the light receivingsection of the solid-state imaging device in the image sensor ADC 2 isblocked from light.

In step ST-40, the pixel signal, output from the solid-state imagingdevice with its light receiving section blocked from light, is convertedinto a digital signal. The signal is then subjected to clamping andother processing before being supplied to the defectdetection/correction circuit 4. Defects are detected and then correctedby the same circuit 4 using defect data. This defect correction iscarried out, for example, according to the process steps ST-14 to ST-22in the flowchart of FIG. 5.

As described above, a defect detection and correction operation iscarried out when video recording is not required during normaloperation. This ensures that the display image is not affected by thedetection and correction operation.

FIG. 8 illustrates a flowchart for describing the static defectdetection and correction of the imaging system 100A during the mute orstill operation for a mode transition.

A description will be made about the defect detection and correctionoperation performed when the mute or still operation for a modetransition starts with the elapse of a predetermined time set by thetimer counter.

In step ST-50, when a predetermined time set by the timer counterelapses, the defect detection and correction operation associated withthe mute or still operation begins for a mode transition of the imagingsystem 100A.

In step ST-52, the controller 30 of the imaging system 100A supplies acontrol signal to each of the functional blocks. The controller 30 alsosupplies a control signal for defect detection and correction to thesignal processing section 5. At the same time, the video signal outputis held.

In step ST-54, the controller 30 determines whether a request has beenmade for defect detection and correction operation. This request is madeautomatically by the controller 30 when an operating time set by thetimer counter of the imaging system 100A elapses as described above.Alternatively, the request is made by the user as he or she manipulatesthe control button provided on the imaging system 100A. It should benoted that means of making a request for defect detection and correctionoperation are not limited to the above.

In step ST-54, when a request is made for defect detection andcorrection, the defect detection and correction timing is detected. Forexample, it is detected whether the mute or still operation is on for amode transition during the operation of the imaging system 100A. Whenthe mute or still operation is on, the controller 30 supplies a controlsignal to the iris mechanism of the lens 1, thus closing the iris. Thisblocks the light receiving section of the solid-state imaging device inthe image sensor ADC 2 from light (ST-56).

In step ST-58, a pixel defect rate of the solid-state imaging device(element) of the image sensor ADC 2 is estimated for the operating timeof the imaging system 100A from statistical distribution. Based on theestimated ratio, the defective pixel count (defect count) is calculatedin the total pixel count of the solid-state imaging device of the imagesensor ADC 2. Based on the calculated defective pixel count (calculatedcorrection count), a threshold value is found which takes into account apermissible pixel count. Then, the defective pixel count is comparedwith the estimated threshold value. When the defective pixel count issmaller than the estimated threshold value, there is no overcorrection.Therefore, normal correction will be performed. In the case ofovercorrection because of the defective pixel count greater than theestimated threshold value, overcorrection will be suppressed.

On the other hand, during pixel defect correction, image data stored inthe memory 20 of FIG. 6 is displayed. This ensures that the on-screenimage is not affected by the defect detection and correction operation.

In step ST-60, when there is no request for defect detection andcorrection or when the defect detection and correction operation in stepST-58 is terminated, the mode transition operation is performed. Themode transition operation is terminated at the completion ofpredetermined operation (step ST-62).

As described above, the defect detection and correction operation isperformed during a period when no video recording is required, whenvideo may not be recorded continuously or when video is kept static.This ensures proper defect correction at all times while at the sametime preventing loss of video signal.

Further, video during the defect detection and correction operationduring which light is blocked is interpolated using a memory. Thisallows for static defect detection and correction without causing anydiscomfort to the user during the operation of the imaging system.

Although a defective pixel detection and correction operation using astatistical method has been described in FIGS. 7 and 8, the presentinvention is also applicable to a normal defect detection and correctionoperation which does not employ any statistical defect correction.

As described above, the defect detection/correction circuit and imagingsystem of the present invention rely on static defect detection andcorrection to calculate an appropriate defective pixel count over time,thus suppressing overcorrection. The pixel defect rate varies dependingon the installation location of the imaging system. However, use of adefect rate and threshold value for overcorrection determination makesit possible to suppress overcorrection properly according to thelocation of use.

Further, static defect detection and correction operation is performedduring a mode transition period such as during the mute or stilloperation. This ensures proper defect correction at all times while atthe same time preventing loss of video signal.

Still further, even if the imaging system is installed wherereadjustment is difficult, it can be readjusted at a proper time thanksto issuance of information. Once installed, the imaging system does notrequire readjustment of its defect detection and correction. The imagingequipment is capable of self-recovery by itself.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A pixel defect correction device comprising: pixel defect detectionmeans configured to (i) receive a pixel signal, (ii) detect defects ofthe pixel signal, and (iii) measure a defect count; timing means; and anovercorrection calculation section configured to (i) compare a measuredvalue of the pixel defect detection means with an estimated value of thepixel signal after the elapse of a predetermined time measured by timingmeans, (ii) determine whether the defect correction is anovercorrection, and (iii) generate a control signal for correction ofthe pixel signal if the pixel signal is the overcorrection; wherein, thecontrol signal generated by the overcorrection calculation section isused to correct defects of the pixel signal, and the overcorrectioncalculation section includes defect distribution calculation meansconfigured to (i) find a pixel defect count from a defect rate, and (ii)estimate a pixel defect count after the elapse of a predetermined timemeasured by the timing means.
 2. The pixel defect correction device ofclaim 1, wherein the overcorrection calculation section includesthreshold value setting means, and the threshold value setting means isconfigured to add a permissible value to the estimated value of thepixel defect count after the elapse of a predetermined time measured bythe timing means to set a threshold value.
 3. The pixel defectcorrection device of claim 1, wherein the overcorrection calculationsection includes a overcorrection determination section, and theovercorrection determination section is configured to (i) compare adetected defective pixel count and the threshold value and (ii) generatean overcorrection control signal if the defective pixel count is greaterthan the threshold value.
 4. The pixel defect correction device of claim1, wherein the overcorrection determination section is configured togenerate an overcorrection control signal so that information is issuedabout correction of defective pixels.
 5. The pixel defect correctiondevice of claim 1, wherein the overcorrection calculation sectionchanges the position of a captured image to determine whether pixels aredefective.